In recent years the use of automated cassette changing devices in central dictation systems as opposed to endless loop dictation/transcription devices has become increasingly popular. An example of a central dictation system employing cassette devices is shown in U.S. Pat. No. 4,024,354 to Bolick et al. which is assigned to the assignee of the present invention.
While such devices have many advantages over previous recording/transcription units, the necessity of moving a plurality of discrete cassettes from an input store, to a recording position in engagement with a relatively complex mechanical tape transport, and then to an output store has required fairly complex electronic controllers as well as finely machined, and therefore expensive, mechanical parts. It has been particularly troublesome to provide apparatus for moving the cassettes through the above-described path while maintaining the ability to stop the cassettes at particular locations within acceptable mechanical tolerances. An example of a cassette changing device in which the mechanical spacing and alignment of the apparatus which transports cassettes is rather critical is shown in U.S. Pat. No. 4,071, 857 to Whitney et al. A controller for the device shown in the Whitney patent is shown in U.S. Pat. No. 4,099,209 to Sander et al.
Applicant's co-pending application Ser. No. 078,232 filed Sept. 24, 1979 entitled CASSETTE CHANGING METHOD AND APPARATUS discloses an improved cassette changing device employing a combination of positive drive and "soft" (spring and clutch coupled) drive to different mechanical components of the changer. Said application also discloses a controller for the device which will attempt to repeat certain portions of a change cycle and to take corrective action in the event that a failure to complete a portion of a change cycle has taken place. Since the preferred embodiments of the present invention shown herein are usable with the mechanical apparatus disclosed in said co-pending application, Application Ser. No. 078,232 filed Sept. 24, 1979 is hereby incorporated by reference exactly as if said application were set forth herein in its entirety.
By using a combination of positive drive and soft drive, as set forth in said Application Ser. No. 078,232, cassette changing devices which employ motors which turn even in the presence of a jammed condition have been constructed. Therefore, it is possible to employ controllers which do not depend on the amount of time which has elapsed between events but only upon angular movement of a motor shaft or a similar physical quantity.